From cddcf852c2102fb622206c63027b8348245b42b0 Mon Sep 17 00:00:00 2001
From: Eugene Burkov <e.burkov@adguard.com>
Date: Tue, 29 Mar 2022 16:21:22 +0300
Subject: [PATCH] cherry-pick: aghnet: fix catching timeout errors

Merge in DNS/adguard-home from fix-is-timeout to master

Squashed commit of the following:

commit b0fefd01f27a835a34e44beb2eb2c34027960a51
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Mar 29 15:57:06 2022 +0300

    aghnet: fix catching timeout errors
---
 CHANGELOG.md                 |  4 ++++
 internal/aghnet/dhcp_unix.go | 39 +++++++++++++-----------------------
 2 files changed, 18 insertions(+), 25 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8b89c6b3..6c09d44e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -74,6 +74,10 @@ In this release, the schema version has changed from 12 to 13.
 
 - Go 1.17 support.  v0.109.0 will require at least Go 1.18 to build.
 
+### Fixed
+
+- I/O timeout errors on checking another DHCP server.
+
 ### Removed
 
 - Go 1.16 support.
diff --git a/internal/aghnet/dhcp_unix.go b/internal/aghnet/dhcp_unix.go
index fd2b9b93..4791d0e5 100644
--- a/internal/aghnet/dhcp_unix.go
+++ b/internal/aghnet/dhcp_unix.go
@@ -156,7 +156,7 @@ func tryConn4(req *dhcpv4.DHCPv4, c net.PacketConn, iface *net.Interface) (ok, n
 	b := make([]byte, 1500)
 	n, _, err := c.ReadFrom(b)
 	if err != nil {
-		if isTimeout(err) {
+		if errors.Is(err, os.ErrDeadlineExceeded) {
 			log.Debug("dhcpv4: didn't receive dhcp response")
 
 			return false, false, nil
@@ -176,20 +176,21 @@ func tryConn4(req *dhcpv4.DHCPv4, c net.PacketConn, iface *net.Interface) (ok, n
 
 	log.Debug("dhcpv4: received message from server: %s", response.Summary())
 
-	if !(response.OpCode == dhcpv4.OpcodeBootReply &&
-		response.HWType == iana.HWTypeEthernet &&
-		bytes.Equal(response.ClientHWAddr, iface.HardwareAddr) &&
-		bytes.Equal(response.TransactionID[:], req.TransactionID[:]) &&
-		response.Options.Has(dhcpv4.OptionDHCPMessageType)) {
-
-		log.Debug("dhcpv4: received message from server doesn't match our request")
+	switch {
+	case
+		response.OpCode != dhcpv4.OpcodeBootReply,
+		response.HWType != iana.HWTypeEthernet,
+		!bytes.Equal(response.ClientHWAddr, iface.HardwareAddr),
+		response.TransactionID != req.TransactionID,
+		!response.Options.Has(dhcpv4.OptionDHCPMessageType):
+		log.Debug("dhcpv4: received response doesn't match the request")
 
 		return false, true, nil
+	default:
+		log.Tracef("dhcpv4: the packet is from an active dhcp server")
+
+		return true, false, nil
 	}
-
-	log.Tracef("dhcpv4: the packet is from an active dhcp server")
-
-	return true, false, nil
 }
 
 // checkOtherDHCPv6 sends a DHCP request to the specified network interface, and
@@ -275,7 +276,7 @@ func tryConn6(req *dhcpv6.Message, c net.PacketConn) (ok, next bool, err error)
 
 	n, _, err := c.ReadFrom(b)
 	if err != nil {
-		if isTimeout(err) {
+		if errors.Is(err, os.ErrDeadlineExceeded) {
 			log.Debug("dhcpv6: didn't receive dhcp response")
 
 			return false, false, nil
@@ -318,15 +319,3 @@ func tryConn6(req *dhcpv6.Message, c net.PacketConn) (ok, next bool, err error)
 
 	return true, false, nil
 }
-
-// isTimeout returns true if err is an operation timeout error from net package.
-//
-// TODO(e.burkov):  Consider moving into netutil.
-func isTimeout(err error) (ok bool) {
-	var operr *net.OpError
-	if errors.As(err, &operr) {
-		return operr.Timeout()
-	}
-
-	return false
-}